Physicist: Classically (according to Newton) kinetic energy is given by 
The difficulty comes from the fact that Newton’s laws paint an incomplete (and ultimately incorrect) picture.
Any object with mass travels slower than light and so may as well be stationary (#1).
Anything with zero mass always travels at the speed of light. But since the speed-of-light is always the speed-of-light to everyone (#2) there’s no way for these objects to ever be stationary (unlike massive stuff). Vive la différence des lois! It’s not important here, but things (like light) that travel at the speed of light never experience the passage of time. Isn’t that awesome?
The point is: light and ordinary matter are very different, and the laws that govern them are just as different.
Light and Matter: different
That being said, in 1905 Einstein managed to write a law that works whenever: 
For light m=0, so E=Pc (energy and momentum are proportional). Notice that you can never have zero momentum, since something with zero mass and zero energy isn’t something, it’s nothing. This is just another way of saying that light can never be stationary.
Also! Say you have an object with mass m, that isn’t moving (P=0). Then you get: E=mc2 (awesome)!
Unrelated tangent: It took a little while, but the laws governing the massive and the massless are even more inter-related than the ‘Stein originally thought. He figured out that the energy of a photon is related to it’s frequency (E=hf), but why are photons so special? Why do they get to have frequencies? They’re not special. Years later (1924) de Broglie drew the most natural line from Einstein’s various equations from light to matter. 
On the off chance that anyone out there got unduly excited about that last statement: the frequencies never go out of wack, you can’t tune them, more importantly they are utterly unimportant on the Human scale, or even the single-cell scale, and don’t ever buy a bracelet or anything else with “quantum” in the name.
No, no, no, no, no, no, no, no, no.
Hello. Why sunlight cannot escape the black hole, when it doesn’t have mass? If black holes gravity wants to influence on sunlight, sunlight should have some mass.
I think mass of light is just extremely small, because if you turn equation around, you get m=E/c^2, which is something very small.
Thanks for all replies 🙂
Elaine-yes on the Faraday cage, interesting thought. Careful with the caulking though…
And yes, photons are “bundles of energy” just as particles with mass are bundles of energy (locked, somewhat) provided by the Higgs boson within the Higgs Field. Light is bestowed its energy vis a vis motion through the electromagnetic field. The motion gives it kinetic energy which is pure and massless when not at rest (at rest it disappears since it is produced kinetically). Particles with mass are massless too when not interacting with the mysterious Higgs field that apparently permeates space and it is this field and its, until recently, hypothesized but not confirmed existence that was inferred by the Standard Formula’s suggestion that all particles should inherently be massless without a catalyst to impart it. Why photons are unaffected by Higgs remains unanswered.
This question of light and gravity is very poorly addressed in school, unless you go for a PhD in Physics. They really ought to explain it better. This board and many like it are testament to the failure of our educators to present such a cardinal aspect of our universe intelligibly, but I’ll bet most teachers couldn’t answer it themselves.
To wit:
1) Light in all its forms has no rest mass.
2) Light does not exist at rest. (This is why we can’t weigh it to be absolutely sure 😉
3) Light behaves as a wave unless interfered with (examined. This can be by camera film or ccd, photon detector, measurement of any kind that would reveal any effect of light or it’s position/velocity)
4) Light behaves as a particle when examined (the examiner can be a metal plate)
5) Light is affected by gravity only in the sense that it’s straight path through curved 4-D spacetime appears to 3-D observers as bending towards objects with large mass. This would occur regardless of whether kinetic energy was present, everything that travels through space must traverse the mass-warped portions as the substrate dictates.
6) E=mc2 is not the whole equation, it is what the media presents for simplicity. A closer approximation is E=mc2+hf with hf determining the kinetic energy.
7) Particles with rest mass (higgs mass) can’t travel at light speed because any amount of mass would consume the entire universe at that speed due to the relation between “c” (300m k/s or “light speed”) and infinite mass. This is made impossible by physical laws which require infinite energy to attain light speed for even a single proton. Energies required to move a proton in the LHC beams require exponentially higher energies for incrementally smaller increases in speed.
8) Light gets from point A to point B by using every possible path between the two points including circling behind your head and then Pluto and then Alpha Centauri and then back to the tree in front of you. You only see the result that probability suggests is the most likely path it should take. (E.g., when you shine a light at a tree, occasionally one photon hits Pluto). If this makes sense, you need to reread that. And youtube some Richard Feynman lectures.
9) Time does not exist for light and if you were going along at 300m k/s you wouldn’t be notice time’s passage either. (You might notice that your body filled the entire universe all of a sudden and since time is a physical property within our universe, it wouldn’t matter since there is now no other reference frame to express time relative to you).
10) Light only moves at “light” speed (c) in a vacuum, otherwise it is slowed down by bouncing off electrons (light is negatively charged too). This bouncing can be predicted and quantified by using Richard Feynman’s “arrows of light” tool discussed in his lectures which you can find referenced on his wikipedia page. Fascinating stuff for the curious.
In Newtonian gravity there is attraction to mass, but not so in General Relativity. Recall that Einstein described gravity not as any kind of force but a warping of spacetime. My favorite analogy is of a trampoline. That’s space, nice and flat. Put a bowling ball on the edge and see it roll to the center. A bowling ball rolling in space. When it comes to rest in the center, it has warped the trampoline surface somewhat. Enough so that when we place marbles or ball bearings on the edge, they roll down and “stick” to the bowling ball. That’s us on Earth. Ball bearings stuck to a bowling ball. And yet no force caused us to stick, it is what happens to the trampoline surface when a weight (mass) is introduced. Now while light cannot warp space, it still must follow the curvature like anything else. And where, like in the case of black holes, that curvature is so extreme it actually wraps back around onto itself, there is nothing to do but follow the circle of no release.
That Einstein was pretty clever, we ought to give him some kind of recognition. An award, perhaps.
Unbelievable that hypothetical Bose-Einstein photon condensate has energy signature and doesn’t have mass. Does it mean even in gravitational field of black hole those condensate will stay where it forms? I do remember read about experiment that prove Einstein’s E=m*C^2. They heat massive object and measure dm=dE/C^2. I heard about modern materials with big dielectric conductivity that allows light travel with speed = 60km/h. Does anybody did similar experiment with light trapped inside big coil made of those materials?
Nikola Tesla. But he ain’t talking.
And I agree that the energy component of a photon sounds like a joke when you first hear it. But let it settle a while. It does make sense.
The explanation doesn’t seem to have answered the question. It asserts that they have no mass, but doesn’t prove it as far as I can see. And the statement that things like light that travel at the speed of light don’t experience the passage of time is ludicrous in my opinion. First, only light travels at the speed of light as far as we know. Second, if light travels at a particular speed in order to get from point a to point b then there is a passage of time. Third, since no one has actually traveled at the speed of light, what one might “perceive” is purely a hypothetical concept and not based on observational science. I honestly think all that we know about light, the speed of light, and time/space is more than likely very different from the reality.
Actually protons should have some mass orelse, it is impossible to have momentum as momentum doesn’t work with zero mass(p=mv)…….simply momentum(p)=force(f) ;can u guys believe that a force would be exerted with zero mass (I.e; f=ma) since m=0…..f=0×a ….f=0, hence without mass, protons possess no momentum(p/f)……A/Q Einstein derived a body of mass 1kg can converted into 90,000,000,000,000,000 joules that is a lot of energy only for converting 1kg of mass……thus ,how much light energy can it be possess in one proton?so it seems too negligent mass for a beam of light and moreover protons are more much tiny than an atom! [impossible n unbeleiveable with no mass and possess momentum(p/f) cuz…..zero is zero(nothing) result of p/f will be always zero]
@Tommy Scott: First, there are also gluons with zero rest mass. Second, there will be no passage of time for the light to get from A to B since point A and point B will be the same place. Third, those explanations based on what we can observe, not just made up.
@Tommy Scott
It gets proven and reproven every day (that light has no rest mass). The LHC proves that not even the tiniest particle of mass (e.g., a proton) can go the speed of light regardless of how many trillions of electrin volts we muster behind it. The more energy we add, the smaller the payoff as we were able to achieve 99.9% light speed a long time ago and have since doubled the power to minimal effect (the useful effect is that by adding more energy, the collider produces higher-mass particles in collisions.
So that demonstrates the fact that any mass seems to have a speed limit just shy of light speed. The fact that light is always measured at light speed gives you the (rest) mass right there: zero. Necessarily.
And as for the time it takes light to get from point A to point B, it is relative to the observer. I know that from our perspective light takes time to travel distances we perceive. About 300,000 kilometres each second. But if we use light itself as the observational frame of reference (impossible to actually test, of course, as light has no way to tell us and we have nothing that can tag along at that speed and report back) … But theoretically, from the information we have about the nature of light, time and space: no time has passed from the reference frame of light.
Nor could it! Because light travels purely in the “space” dimension of spacetime. Space and time are equivalent just as energy and mass are equivalent. Take some energy and create mass with it (LHC) and you lose the correlating amount of energy in the mass formation. Conversely, turn mass into energy (burn a log) and you lose maas in direct correlation to the energy produced.
Time and space have similar trade-offs. In spacetime, both space and time perception are determined by how fast you are moving relative to an observer. If I am boy moving in space, I am therefore hurtling through spacetime solely in the time dimension. I am going the equivalent of light speed through time. We all do this. Every molecule in iur bodies are moving at all times (so we don’t violate Brownian Motion and cease to exist) but for purposes of spacetime: we are going as fast through time as possible and virtually none through space. If we hop in a spaceship that can go 90% the speed of light, we are now going through spacetime with only 10% dedicated to the time dimension which means time slows down for us (relative to slower moving observers)
by an equivalent amount. So, for light, using 100% of the speed of light, there is nothing being used in the time dimension so time is not a part of light’s eternal journey through spacetime. A journey that, FOR LIGHT, never actually begins or ends.
@Alex, why do you say point A and point B are the same place? They are different points, hence the reason they are labeled A and B. And no you cannot observe travel at the speed of light from the reference frame of one traveling at that speed. You are observing it as an outside observer. Back to square one.
I CAN PROVE THAT LIGHT HAS WEIGHT
no photons has weight because of einstein statement energy mass equilense we can say that photons have mass and energy
photons have mass beacuse of einstien statement and by influence of gravity on photons we can say that photons have mass
It is wrong beacuse light carry photons which have energy and momentum with this we can say light carry energy with it.
I am thinking that, because I have always believed that on some level, photons have mass – we may need to be in a black hole to see this for ourselves. Mathematically can we prove the mass bearing photon? That is, it’s much more believable once it is proven in math – we can understand the mass bearing photon. When one gets an X-ray, mammogram, ultrasound, etc., one cannot feel any intrusion of photons. That’s why I think we have to perhaps be in a black hole to see this for ourselves – the black hole seems like a great proving ground for this concept.
All black holes are filled with confetti made from shredded pistachio shells and left over from the black hole raves that take place forever unless you get there late which would be any time after they start (black hole mass > maximum gravity to experience time dimension). The rave begins precisely at critical mass for singularity status which means you need to get there right when time stops. Too soon, and you join the confetti as a non-sentient, non-observer. But you aren’t missing much since nothing can happen since without time no events can occur. Unless… you factor in THE COMPLETE SUSPENSION OF ALL PHYSICAL LAWS OF THE UNIVERSE!
You heard right, singularity fans! All physics breaks down at the point of the singularity. All math results in zeroes or infinities from our frame of reference, which can only be used on our side of the event cone. Our physics does not apply outside the event cone! Anything can be going on in there. Sexual deviance, no doubt, is being practiced with abandon. Armani suits being sold for ridiculous prices out of the back of Roman chariots. Free chameleon tongues for all.
And light? Well you can pick it up, a photon at a time. pet it. ask it questions. tickle it. name it elmo. but there’s only one way out. and it’s often a long wait. you can only escape the event horizon by becoming hawking radiation. and the odds of a black hole releasing even one intact molecule let alone all your molecules lined up correctly is about one chance in zero in a billion trillion years. normally they just burp an electron here or there. so wear something warm (i guess. who knows?) and bring your ungulflazer (you will understand later when it’s too late to build one).
Happy trails!
Well done tintweezl
One more question, why does light, when it’s slowed down take on a mass, as in the Einstein-Bose condensate?
Gojko:
E = mc^2 only applies to non-moving objects.
For moving objects, we have E = γmc^2 where γ depends on speed. And for objects with the speed of light, γ = ∞. So light cannot have a mass.
the answer I got was not satisfying. It is said that everything has mass. Nothing is massless. Then how come photon does not have mass,even when a photon is moving at the speed of light.
“It is said” where?
“It is said that everything has mass.”
Whoever said that clearly doesn’t understand physics.
@Thomas B the speed f light is not infinite
@markc:
γ = sqrt(1/(1-β^2))
β = v/c
If an object is moving at the speed of light, then β = 1 and γ = ∞.
Please explain Thomas B’s equation- posting of 5/6/16. Does this favor the photon being mass bearing?
Light has the very high velocity but the mass of photon is very very less that why the force due to light get tends to “0” but the photons has the mass….
For everyone arguing E=mc^2 => Photon has mass, since it got energy.
The complete equation is E= Mc^2 + hf. In everything above atoms hf —-> 0.
This explains Zero mass and non-zero energy of Photon.
Hence the saying, partial information is dangerous.
Mathematically,
E= hf. (Einstein)
For light, E= hf. (Plank’s constant times it’s frequency.)
What about Momentum?
Momentum is a quantity of motion in an object. Light, I’m sure you all would agree, has a lot of motion.
Mathematically,
E^2= P^2C^2 + M^2C^4
For photon, M=0,
E^2 = P^2 x C^2
=> E=PC
also E=hf
hence,
hf=PC
=> P=hf/C
P is momentum.
Energy is capacity to do work, and momentum is quantity of motion.
Light by virtue of its velocity can do work and has motion.
Philosophy: (understanding the equations)
Any mass (no matter how insignificant) moving at the speed C will occupy the entire universe.
To understand how something can occupy the entire space with a given velocity, consider this:
Everyone has seen a fan I guess. When you see a moving fan, you don’t see the blades, you see a disk. Because at the speed of rotation, the blades occupy all the space at all the time, hence we see a disk.
In a similar way, anything with a mass and moving with velocity C will occupy all the space and at ALL THE TIME.
At “ALL THE TIME” is a tricky statement, because light doesn’t know time.
Let me explain why light must not experience time. And what it means to say “at all the time.”
First, let’s define Time:
1 hour is the time it takes for the hour hand to move one unit; or the time it take a car travelling at an average speed of 60km/hr. for one hour to travel a distance of 60 km.
But the definition has a problem: I cannot define time by using time in my definition.
Let me try another way:
Time is the relative difference in observable velocity. What it means is, if you can see/observe any motion, then there is time that exists for you. Time is relative to the observer and cannot exist independent of motion (relative motion) and observer. T=d/v. d is distance, v is velocity. Anything that is moving must change its position and have a non-zero d. So, if you can observe velocity, d exists for you, and (using the equation) time exists for you.
Now what does it really mean when we say time doesn’t exist for the light?
As I said, time is the relative difference in observable/observed velocity. (Observation is relative to the observer.) If we can prove that relative velocity doesn’t exist for light i.e., it cannot see anything moving (not even itself) then we will prove that time don’t exist for light.
Let’s go to the reference of a light, call it L, and see what it might observe.
Relative to L (assuming L sees itself as at rest) everything else (assuming L can differentiate b/w itself and other things) will seem to be moving at the speed C (C+x=C, also C-x=C, x is the speed of thing L observes in their frame of reference). This is simple relativity. L would observe me moving at the speed of light, C. Given that I have a mass, an undeniable truth, moving at speed of light I will become energy (e=mc^2), no matter the amount of mass I carry. Everything else that has mass will be energy too in the reference of light. (Assuming nothing is mass-less) Hence, everything will become the same thing. L won’t be able to distinguish between anything. To L everything will look the same.
Now, the question is will this other thing (everything else) will be something different than light or light itself, to L.
Light is defines is something that moves with a velocity C, because all it has is velocity (no mass) and at rest it ceases to exist. Therefore, anything moving with the speed of light must be light itself.
Hence, L will not just see everything to be same, it will see everything to be same as itself. This implies, L won’t see anything at all, because everything is L and L is everything.
If you can’t differentiate between two things, you can observe their relative velocity.
Hence, there will be no relative velocity for L. For L everything (which is itself) will be at rest, at ZERO and at all the “time”. In it’s frame of reference, Light, L, is at ZERO velocity and at all the “time”.
Just to recall, by the analogy of the Fan, if light had any mass, then it would ideally occupy all the space. ——— 1
Also we argued that time doesn’t exist for light. —— 2
From 1 & 2,
Light (L) if it had mass would occupy all the space at all the time.
Let’s argue the same thing in a way that can be challenged experimentally:
If light has some mass, then that would mean that photons has mass. If this was true, then it would be possible to create a laser beam with extremely high density of light (we can talk about density if there is a mass) and then measure it’s weight. (Infinitesimally small quantity when added infinitely would generate something that is not infinitesimally small.)
Another way would be to slow the light in a bose-einstein condensate and then observe the weight of the entire thing. If light has mass, then Gravity will give it weight.
A photon is said to have no rest mass.
According to De Broglie matter can and does exist as waves. But photons can exist as waves. Therefore photons have matter.
Mass is the amount of matter. But light is said to have no mass meaning no matter. But this is false. Photons have matter and perhaps it would be better to say light or photons have no rest matter
That it has matter could be demonstrated by the last paragraph in the above comment, and by the facts that light has potencies and under the right conditions gives rise to a positron and electron possessing different matter and different forms along with being in a solid state. And the reverse can occur with the positron and electron uniting, losing their forms, and giving rise to a different kind of matter with a different form, a particle that can exist in a wave form as well. Notice that the solid state is lost.
Should one consider this particle wave form duality a new state since it is not considered to be a solid state?
Notice also that it appears that the positron and electron exist virtually within the photon just as hydrogen and oxygen exist virtually in water.
Just as water under the right conditions does yield oxygen and hydrogen so a photon under the right conditions does yield two particles each with different matter and both in a solid state.
At this level of reality one might reconsider the Aristotelian doctrine of matter and form.
Accordingly to De Broglie matter behaves also as waves. Photons can and do behave as waves. Therefore photons have matter. How much?
What is the matter or stuff of a photon- mystery
What is the matter or stuff of any particle- mystery
By mass we mean the amount of matter of a thing. Mass is a measure. It is not the matter.
It is impossible that a photon have no mass as the term is being thrown around. Instead of saying that a photon has no rest mass it would be more correct to say it has no rest matter and in this instance exclude the confusing term mass. But it still has matter.
A photon does not have mass in the Newtonian sense and the term should be avoided.
Photons have matter just as neutrinos do.
We also know photons have matter because they have potencies and under the right conditions give up a positron and electron; and under the right conditions
a positron and electron unite to give a photon. Notice that the positron and electron that are given up have matter of a different kind and form and are in a solid state. Perhaps wave particle duality might be considered another state of matter.
The electron and positron are in the photon virtually just as hydrogen and oxygen are in water virtually.
When the matter of the solid state of the positron and electron unite, a photon, that can exist in a wave form comes into existence with its own different matter existing in a new way.
Also worth noting is the last paragraph in the above comment.
At this level of magnitude perhaps there is room to reconsider the Aristotlian doctrine of matter and form.
1) First you say that matter is waves. Then you state a photon has waves. Then you state that a photon is matter as if you just proved it. That is like me saying that fish have tongues, you have a tongue, you are a fish.
2) Matter’s exact definition is: “anything that occupies space and has mass”. So, no, Mass is not the amount of matter. Neither is it “false” to say that light has no mass and therefore no matter. It is not matter without mass. It’s a perfect example of non-matter (as opposed to anti-matter). Photons do not “have matter” and it seems you have some confusion as to the definition of matter since all matter means is, once again, something that occupies space and has mass. You act like it’s a separate thing that imbues mass to otherwise massless particles.
3) The creation of electron/positron pairs from light with a frequency high enough to equal the mass/energy of 2 electrons is a great example of how light has ZERO rest energy but only inertial energy. Please understand the distinction between M in reference to something not moving and inertial mass. Something with zero rest mass is moving along with a frequency, or hf energy, of say 1.5222 MeV. It takes 1.0222 MeV to make a pair of electrons so a Positron and Electron are produced, each moving with the energy of 0.25 MeV — the .5 remainder split between the two as inertial mass/energy. So we have an annihilated photon with zero rest mass shedding its inertial mass-energy to create two NET ZERO REST MASS PARTICLES (since electron and positron have zero net rest mass as they are antimatter of each other). The remaining .5 MeV is converted into kinetic energy, converted into momentum of the two particles and obeying the conservation of energy laws. So the positron and electron are not constituent components of an electron like hydrogen and oxygen are to water. Spontaneous events where positron/electron pairs are created happen when nucleus energy exceeds 1.022 MeV without a photon to provide it.
4. At this level of reality we may go back and hit the books to recondition our basic physics understanding.
So I was thinking, can a object exist as both energy and mass at the same time?
After all the arguing over politics I endure on Twitter and FB, this was a nice distraction. The argument put forth about light experiencing no time dimension due to its 100% commitment to space was pretty strong.
It seems that from its perspective, the moment a photon is emitted, it is both everywhere and everywhen in the universe. Is it’s perception limited to our universe, or does its perception extend throughout the multiverse?
A photon’s perception is limited to a straight line, namely the path it travels. From its perspective, there is no time: it vanishes from existence the moment it appears.
”photon can exert pressure and force”from this statement photon should have mass because only the substance with mass can exert pressure and force.But also photon is not affected by gravitational field means it does not have mass because only those substance is not affected by gravity which has no mass.then actually it has mass or no mass.
And Anil, I also find it interesting about photons: force exerting. They are noted to have momentum. Interesting too that photons are “assigned” a “rest mass” I believe, because they at never at rest. But it is interesting to me that the idea emerged to assign a rest mass number, a quantification, in order for the photon to be used in an equation. I find it completely believable, and I am not a physicist, chemist, or any other expert in the field, that photons have mass. In some arena, somewhere. Can you imagine being assigned the task of catching random photons, them grabbing an individual photon in hopes of studying the photon?!
the rest mass is zero means what?rest mass of photon is given by.( M•=m√1-v*2/c*2)so from this equation to be rest mass zero the velocity of partial should be =to velocity of light (I.e. v=c)so in this case the mass is not in rest so why? It is called so
So..this photon as a mass bearing entity intrigues me for a singular reason. When I studied X-ray technology (no…I didn’t go on to become an X-ray tech) I knew that whenever I shot an X-ray, a snapshot in which I collimated, or focused the aperture to concentrate the photons, the photons passed through the target. Let’s say….an apple because I do not remember X-raying anything human during that time. So once exiting the apple, at the speed of light, the photons were “stopped” by the metallic surfaces they encountered, the film case in that example. First,…I can only assume the photons were stopped. Secondly…as there was no hole left in the apple I can assume I didn’t *hurt* the apple : I didn’t force a packet of mass bearing photons through an apple causing a distinctive path in its wake. But I started to wonder, on what scale would the mass bearing photons LEAVE a hole in their wake? Obviously I controlled the milliamperes and the kilovolts in this X-ray exercise by dialing in the required amount of penetrating radiation- an ionizing blow, enough to provide an X-ray photo of the apple. Now…granted….it is noted in my text (now well worn…I did this a decade ago) that radiation can be quantifiably exuded from the apple, a kind of radiation “glow” without a real glow. But the X-ray beam was brief, my finger is not still on the button, and I presume the beam was effectively stopped. But at such low energies the ionizing radiation cannot be “felt” in the X-ray room.. there’s no residual. The only smoking gun was the X-ray or photo I obtained within the film plate. So I began to envision a situation in which ionizing X-radiation (photon packets, to break it down) COULD leave a hole through the “apple.” Perhaps during a supernova? Perhaps during my local nuclear power plant’s meltdown and ensuing loosening of gamma radiation (X-radiation along for the ride), or just in some other catastrophic mega release of photons? I just believe the photons will show themselves as mass bearing critters who have just revealed their secret . I believe that somehow there’s an example of how the X-ray can deconstruct something because they were mass bearers who muscled their way trough something due to their light AND mass bearing capabilities.
For David Smith: I realize that a bolt of lightening is a discharge of electricity. Bonus to us lightening watching folks like myself..we get to see light. But electricity moves at the speed of the electron which is a quantified, a finite number. Any physics text will provide the reader a measure of the electron’s speed. Lightening is created because nature likes to keep balance: storm cloud kinetic energies cause changes in + and – charges – thus a discharge of electricity in order to reset the milieu to a balance.
But I am really enjoying this thread because I see no instance in which a mass bearing electron is “impossible.” I hope readers will notice my other post of today’s date.
Emc^2 is for mass, but light has a different
Equation, light and or lightning are different because light does not have mass,we see lightning from the big discharges of current
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If photons are massless then it should have zero momentum but they are moving with a high momentum as we see, and if also photons are massless then the photoelectric effect of light shouldn’t take place as in that transfer of energy takes place.
You say, “For light m=0, so E=Pc….”
If P = mv, and m = 0, how can light have P?
@Cass
. If you have zero mass, you can still have energy and momentum.
That’s Newton’s equation for momentum. It works in the case of slow-moving objects with mass. The correct equation that works in all cases is
So…now that there is new evidence revealed earlier this year regarding the “bending” ability of the photon, is it time to consider that my original theory of mass-bearing photons is possible? It just seems like there is not everything known of my photon friends and that a possibility of a new ability (sorry, not trying to create a rhyme) of the photon – mass-bearing critters that I believe them to be – is not entirely out of the question. In other words,….is there room in our abstract thinking compartment of our brain to consider the “known” stuff about my photon buddies and also consider that we may discover more about photons ? I hope so.. It seems that the alternative is something of a rut: Classify the photon by what we know or were taught as I was. Much as I learned in high school (long ago, trust me) that Pluto is one of our neighboring planets. Oh….let’s (I hope) not wander down that path. Keep an open mind is the real message here. And how wonderful was it to discover a new twist in the photon ability recently !! And who was out there looking in the first place?
Nothing that travels at constant “c”, or light speed, can have mass. It’s a truth borne out in a thousand empirical demonstrations, confirmation of the Higgs field, speed limit of particle accelerators, and other proofs ad infinitum. Open mind is fine but not at the expense of reason. Elaine, I appreciate that you are excited about this concept since you originally conceived it but…let it go. It’s fundamentally impossible and unnecessary.
I’d like to act as devil’s advocate to @Cass. Not saying the Physicist is wrong but I’d be interested in some clarification. Going back to the top of this question you say “something with zero mass AND [my emphasis] zero energy isn’t something, it’s nothing.” I think it’s rather less than that: “something with zero mass” is, itself and by its very definition, “nothing.”
You point to the equation E=Pc^2 + m^2c^2 and, if I understand you correctly, argue that, because the photon supposedly has zero mass, then, as you say, “For light m=0, so E=Pc.” But P is, itself, equal to mv as you, yourself point out above though relegating it to classical physics. So if m=0, P=0, just as @Cass said and, thus, E=0. Now, if you meant, without saying so, that P is something other than mv at the speed of light please clarify.
I remain to be convinced the photon is anything more than hypothetical, similar to “dark energy,” the latter being an invention of the mind rather than nature to explain the acceleration in the expansion of the universe that physics cannot prove. The notion that energy can be transmitted through space in bundles unassociated with anything tangible, or a force, seems fanciful. (Energy CAN be transmitted through space as work (i.e., product of force and displacement), as, for example, in an electric motor, where the force in motion between the stator and rotor is applied without physical contact between the two.
It all comes down to what “energy” is, really. If energy is the potential to do work, which itself is the potential to displace a force, where is that potential with respect to “the thing that never was,” the photon? If the photon has no mass, it has no gravitational, magnetic or electromagnetic properties to react a force applied through such fields. How could a “particle” of zero mass “impact” atoms to then transfer energy from nothing to something?
Respectfully submitted, devil’s advocate.
@Ross
is an approximation for momentum that works for massive objects traveling slowly. The actual equation is 
for objects with mass and 
for objects without mass.
I should have been more clear.
Thanks for that more precise answer to @Cass’ comment. I still have difficulty accepting that “energy” can exist by itself in empty space. If the definition of “energy” is the potential to do work, where “work” is the product of force and displacement, how can work be effected without an associated mass or force, which I presume photons lack?
Can such unassociated energy exist elsewhere than in photons?
How does a massless photon transfer its energy to a massive atom or subatomic particle?
Where does the photon stand vis a vis other subatomic particles as to confirmation? E.g., is it more than the mere creation of the mind to explain real physical observations?
Thanks
@Ross
Photons are the “force carriers” of the electromagnetic force. When a photon hits a charged particle, it deposits its momentum in that particle (thus doing work on it). They’re definitely not a hypothetical particle. A precise understanding of photons is absolutely indispensable for modern technology (optics in particular). But more than that, we can directly measure the existence of individual photons with extremely sensitive photo-detectors.
Photons were actually among the first particles verified to exist, as they helped resolve conundrums like the “photoelectric effect” and the “ultraviolet catastrophe“.